A label printing apparatus includes a liquid crystal display unit for displaying an input character string and a message corresponding to each operation stage, a printing unit for printing a character string on each label, a storage unit for storing each data, and a CPU for performing each processing and control. Label information specifying sizes and the like of various types of labels, sheet numbers corresponding to the label information, character size information defining character sizes, and the like are stored in the storage unit. The CPU specifies label information corresponding to the sheet number and selects a maximum printable character size from a character size table as an initial value on the basis of a printing area. The character size is changed so that the horizontal length of an input character string falls within the printing area. The character size is further changed so that all the characters of the character string extending in all the lines fall within the printing area. An optimal character size is finally selected, and actual printing is performed on each label using this character size.